Lamp



March 24, 1959 H. c. MCCORMICK LONGACRE 2,879,431

LAMP

Filed Sept. 4, 1956 INVENTOR HENRY C. M LONGACRE MMX ATTORNEY 2 Sheets-Sheet 1 March 24; 1959 H. C. MCCORMICK LONGACRE LAMP 2 Sheets-Sheet 2 Filed Sept. 4', 1956 INVENTOR HENRY C. M. LONGACRE BY 2 v ATTORNEY LAMP H Henry' Clay McCormick Longacre,'Floral Park, NY

assignor to Sylvania Electric Products liic a corpora-. tion of Massachusetts Application September 4, 1956, Serial Nol'6 07,676 4 Claims. (Cl. 313-34i) My invention relates to light producing, devices. In many phases of the lighting itidustryfand' particu-, larly inthose phases whichare concerned with the 'pr'o'jduction of light sources for motion'picture projectors, search lights and the like, it is necessaryto' provide/a quasi-point source of high intensity light in which the visible light spectra approximates that of the sun. ,Conventionally, an arc discharge betweencarbon' or'zirconium electrodes is used for this purpose. The apparatus required for the production of such an arc is complex and expensive; it must be suppliedwith power by special generators; it must be operated by highly skilled technicians. Y

I have devised a new type of lamp for use in PPlications of the above type which does not use an arc. "This lamp can be supplied with electric power directly from an electric power line, and no special generators or similar equipment are required. Moreover, this lamp can be operated automatically and no attend-ants or operators are required.

Accordingly, it is an object of the invention to eliminate the necessity of using carbon or zirconium arcs in producing high intensity light from a quasi-point source.

Another object is to provide a new high intensitylight' source which does not use an arc discharge.

Still another object is to provide a new highintensity lamp containing a light source electrically heated to operating temperature and directly coupled to a conventional single phase alternating current source.

Yet another object is to providea' newzfhighiintensity lamp in which an electrically heated-refractory element is used as a light source, thearea of the light emissive portion of the element being maintained at a substantially uniform temperature.

Still a further object is to replace carbon or zirconium arcs with a light source 'formed from a refractory element electrically heated'to temperatures on the order 6f thousands of degrees Kelvin, the area of the light emissive portion of the element being maintained at a sub stantially uniform temperature.

Yet another object is to provide a new refractory element light source electrically heated uniformly to very high temperatures, the electrical energy being supplied from a conventional single phase source of alternating current.

These and other objects of my invention will either be explained or will become apparent hereinafter.

In accordance with the principles of my invention there is provided a refractory element having a thin central segment and two equidistantly spaced legs attached to corresponding ends of the segment. Current from an electrical energy source, such as a conventional 60 cycle single phase source is supplied through the legs to the center portion to raise the temperature of the segment to such a value (ranging upward to about 4500' K.) that the segment becomes a quasi-point source of light. At these operating temperatures, the spectra of the emitted light approximates that of a carbon or zirconium are.

In order to prevent the legs from being heated to 'an operating temperature at which light emission will be produced (this effect would prevent the segment from acting as a point source), the resistance of the legs must be low relative to the resistance of the central segment, thus concentrating the current heating action in the segment itself. However, if the resistance of each leg is uniform throughout its length, sharp localized temperature gradients will be established about the junction of each leg and the segment, and these gradients will cause internal strains, cracking, and other undesirable surfaceand structural changes.

These undesirable effects are minimized by shapingthe legs in such manner that the cross sectional area of each leg increases with increasing distance from the central segment; under these conditions, temperature gradients are much lessaccentuated and have no detrimental effect. In order for the segment to act as a quasi-point source, the spectra of the light emitted at any selected point on the surface of the segment must be substantially identical with the spectra of the light emitted by any other point on.

the surface; otherwise, the spectra would vary from point; to point along the surface of the segment, thus destroying the point source effect.

However, because the segment is necessarily heated to an operating temperature much higher than the operating temperatures of the legs, heat will flow from the ends of the segment into the legs, and a temperature gradient is established across the segment itself. Hence, the ele ment as described thus far would not act as a quasi-point source, because this gradient, as indicated in the preced ing paragraph, would cause local variations in the light spectra of the segment. In order to eliminatethis gradient and thus permit the segment to act as a true point source, I have found it necessary to increase the resistance at the ends of the segment relative to the resistance'of the remaining por' tion of the segment, forexample, by reducing the cross sectional area of the element in the regionv of each leg segment junction. When the segment is heated to operating temperature, the heat input in these regionsis su-fficiently increased (as compared to the heat input in regions where the cross sectional area of each junction is not reduced) so that the operating temperature in these regions becomes equal to that at the center of the segment, and the entire surface of. the segment is maintained at a substantially constant temperature. Hence, the point source effect is attained.

The element can be formed from one or more conven' tional high purity refractory materials, such' as tungsten, the carbides of tantalum, zirconium' and hafnium'and the like. These materials tend to oxidize rapidly and fail in oxygen containing atmosphere. Consequently, the element is operated in an oxygen free atmosphere, such as argon or other inert gas or a vacuum.

Illustrative embodiments of my invention will now be explained with reference to the accompanying drawings, wherein:

Fig. l is an isometric view of a refractory element light source in accordance with the invention;

Fig. 2 is an enlarged fragmentary detail of a portion of the element shown in Fig. 1;

Fig. 3 is an isometric view showing the refractory element of Fig. 1 together with associated supporting structure; and

Fig. 4 is an isometric view of a demountable lamp in corporating the element of Fig. 1.

Referring now to the drawings, there is provided a re fractory element formed from tantalum carbide and provided with a light emissive thin segment 5, opposite ends 3 of which are attached to tapered legs 2. At the region of each segment-leg juction, the cross sectional area of Patented Mar, 24,. 1959.

the element is sharply and locally reduced, in this example by mcans of a cross sectional groove or channel 1.

Each end 3 of the legs 2 remote from the center section 5 is brazed. to a separate hollow copper block 4. Both copper blocks rest on a ceramic disc 7. Bar springs 6 are set into each copper block for the purpose of holding the refractory element in tension, thereby preventing the element from possible buckling due to thermal expansion of the segment 5.

A pair of hollow copper tubes 8 insulatedly separated from a 'base plate 110 vertically extend upwards from this base plate 116 through the ceramic disc 7 into each hollow copper block. These tubes are spring loaded by springs 160. Each pair of tubes are connected in paral lel to corresponding output terminals (not shown) of a conventional single phase 110 volt, alternating current source, thus supplying the requisite electrical energy to the segment 5.

Water is fed through one conductor of each pair into the associated block, then is fed out of the block through i the other conductor to cool the conductors and the ends of the refractory element.

A quartz envelope 102 covers the entire structure; the bottom flange of the envelope rests on a circular ring 108 fitted within a corresponding groove of the supporting or base plate lit A second circular ring 3106 is placed upon the top surface of the bottom flange and a rubber gasket 104 covers the circular ring 106. An annular clamping section 110, in threaded engagement with the periphery of plate 110, holds the flange, gasket, and associated circular rings tightly against the base plate. The enclosed volume within the envelope is evacuated through an exhaust port in the base plate by means of a conventional vacuum pump assembly (not shown). After the envelope has been completely evacuated, if desired, an inert gas can be introduced into the envelope through the exhaust port.

While I have pointed out and shown my invention as applied above, it will 'be ap arent to those skilled in the art that many modifications can be made within the scope and sphere of my invention as defined in the claims which follow.

What is claimed is:

1. A resistance heated electrode comprising an integral 0 pared to the cross sectional area of the element in regions immediately adjacent each localized region.

2. A resistance heated electrode comprising an integral solid element formed from refractory material, said ele ment being provided with a single, thin, narrow rectangular center portion and a pair of equidistantly spaced legs extending from opposite narrow ends of said portion, the cross sectional area of each leg increasing with increasing distance from said center portion, the flat surface of said center portion being substantially coplanar with the top surface of each of said legs, the localized region about each leg-center portion junction having a V shaped notch extending transversely to said center portion and the corresponding leg.

3. A resistance heated electrode comprising an integral solid element formed from refractory material, said element being provided with a single, thin, narrow rectangular center portion and a pair of equidistantly spaced legs extending from opposite narrow ends of said portion, the cross sectional area of each leg increasing with increasing distance from said center portion, the fiat surface of said center portion being substantially coplanar with the top surface of each of said legs, the localized region about each leg-center portion junction having an electrical resistance which is high relative to the resistance of said center portion, the electrical resistance of said center portion being high relative to the resistance of each leg.

4. A resistance heated electrode comprising an integral solid element formed from refractory material, said element being provided with a single, thin, narrow rectangular center portion and a pair of equidistantly spaced legs extending from opposite narrow ends of said portion, the cross sectional area of each leg increasing with increasing distance from said center portion, the fiat surface of said center portion being substantially coplanar with the top surface of each of said legs, the localized region about each leg-center portion junction having an electrical resistance which is high relative to the resistance of said center portion, the electrical resistance of said center portion being high relative to the resistance of each leg, said center portion and junction resistances having values at which when said element is electrically heated by passing current through said legs, the operating temperature of said center portion is substantially uniform over its surface.

References Cited in the file of this patent UNITED STATES PATENTS 

